An image forming device is conventionally known that is constituted so that a device main body comprises an upper structure and a lower structure, wherein the upper structure is openably and closably provided to the lower structure about the center of a support shaft, and a helical torsion coil spring is provided wound around the support shaft and urges the upper structure in the open direction. According to this device, the shock when closing the opened upper structure to the lower structure is absorbed by the force of the helical torsion coil spring.
Nevertheless, the support shaft constitutes a guide bar of the helical torsion coil spring because the helical torsion coil spring is provided in this device wound around the support shaft, and the shape of the helical torsion coil spring, such as the coil diameter and the wire diameter, is constrained by the shape of the support shaft, such as its outer diameter. Conversely, to ensure the required load of the helical torsion coil spring, the shape of the support shaft must match the shape of the helical torsion coil spring. Namely, mutual constraints arise when designing the support shaft and the helical torsion coil spring, which reduce the number of degrees of freedom in the design. In addition, there is a reduction in the number of degrees of freedom in the design from a layout standpoint because the position of the support shaft is limited to the positions that can support the helical torsion coil spring. Furthermore, the strength of the support shaft must be increased because of the load applied to the support shaft via the helical torsion coil spring when opening and closing the upper structure.
It is an object of the present invention to provide a novel opening and closing device that is capable of reducing the load on the support shaft, and wherein the support shaft and the helical torsion coil spring can be freely designed and disposed without mutual constraints.